In February, a study called ‘The neuroactive potential of the human gut microbiota in quality of life and depression’was published in Nature Microbiology. The researchers found that there seemed to be certain strains of stomach bacteria tied to mental health; people suffering depression were found to have low levels of coprococcus and dialister bacteria, while both coprococcus and faecalibacterium were more frequently found in those claiming a high mental quality of life. The link may be purely correlational, but the study did also find that gut microbes can communicate with the nervous system.

“We studied whether gut bacteria in general would have a means to talk to the nervous system, by analysing their DNA,” said Jeroen Raes, of the Flanders Institute for Biotechnology and the Catholic University of Leuven. “We found that many can produce neurotransmitters or precursors for substances like dopamine and serotonin.”

Another study published in Gastroenterology found that 64% of participants with mild-to-moderate anxiety or depression experienced fewer depression symptoms when taking a daily probiotic for six weeks; by comparison, only 32% of those taking a placebo experienced improvement.

That same study used MRI brain imaging on the participants, finding that those taking the probiotic experienced changes in the areas of the brain associated with mood. They concluded that the probiotic they used, bifidobacterium longum, reduced depressions scores and that the brain activation patterns observed suggested that the probiotic could reduce limbic reactivity (the limbic system of the brain largely governs emotion and the fight/flight response).  

It should be noted, however, that the scientific support for probiotics affecting mental health is somewhat mixed. While the study by Raes and his team examined more than 1,000 people, the Gastroenterology study had just 44 participants.

Furthermore, a 2017 review published in Annals of General Psychiatry examined 10 blinded and placebo-controlled studies into the subject; the studies in question not only all had small participant pools, ranging from 42 to 124 participants, but the results were in disagreement from one study to the next. In the author’s own conclusion, “the clinical effects of probiotics on mental health have yet to be studied comprehensively”.

The review continued: “Gaps and inconsistencies in the research on the effects of probiotics on depressive symptoms make it difficult to confirm evidence of efficacy. Duration of intervention varies widely, as does the quantity and strains of the probiotics, and research is lacking on depressive symptoms apart from mood, anxiety, and cognition, such as sleep. Perhaps most notably are the inconsistencies in defining depression across studies.”

The consumption of probiotics as a mental health aid is unlikely to pose any significant risk to consumers, and may provide some relief, if only as a placebo. Talking to Nicole Beurkens, a licensed psychologist and certified nutrition specialist, Healthline was told that probiotics could safely be considered a supplementary treatment for mental health. It is important, however, to emphasise that, at the current stage of research, they are no replacement for established methods of treatment.

Any manufacturer looking to enter the market should seriously consider the risk of doing so without the requisite research to support any wellness claims. Adding probiotics to their treatment plan is unlikely to do any harm to consumers, but any concrete claim of probiotics acting as a mental health treatment places brands at significant risk of breaching existing regulation, given the current state of research.

Regulation is perhaps the key challenge facing any potential products entering the probiotic market. The body of research suggesting a link to mental health is growing but the evidence is, as yet, scant and occasionally contradictory.

The prospective consumer base is huge: according to MarketsandMarkets the probiotics market is set to reach a value of $69.3bn by 2023, but so are the regulatory risks. Consider that, in 2010, Danonn had to settle charges from the FTC about exaggerated health claims on two of its probiotic products.

Nevertheless, the sector is pushing forward. Researchers are making great strides into further understanding gut bacteria and the effects they can have, and specific studies are benig conducted into the connection between said bacteria and the mind. In February, the Queensland University of Technology announced clinical research into whether an imbalance of the intestinal microbiome could play a role in depression and how probiotics could help manage that condition.

The principal investigator in this study, clinical psychologist Dr Esben Strodl, said: “Participants in the trial will take a combination of probiotics and magnesium orotate, and we’ll be measuring the effects of this on their physical and mental health.

“In previous small pilot studies, probiotics and magnesium orotate were shown to provide positive benefits to people with depression who were not responding to commonly prescribed anti-depressant medications – and we’re hoping to see those results replicated in this larger study.”

In industry, too, products are rolling out under the banner of the gut-brain connection. In March, Nouri capsules became commercially available in the US. The product, which was selected as one of the Probiota event’s two ‘pioneers’, combines five probiotic strains with omega 3, 6, and 9.

Although Nouri makes uses a somewhat roundabout way in marketing how its product contributes to brain health (omega fatty acids are also linked to assisting mental health so it is tricky to assign credit to the probiotics), there is a clear emphasis from the company that it is intended for both mental and physical health. If the product proves successful, it may well be a forerunner for the evolution of the probiotics market.